1. Field of the Invention
The invention relates to a chip bonding process, and more particularly to a process for a patterned underfill being formed in advance of bonding chips.
2. Description of the Related Art
IT products are playing a more and more important role in modern industrial society recently. The function of electronic products becomes much more versatile as the trend renews old-fashion IT products. Their qualities are becoming more stable as well. When it comes to package technology, in order to possess better performance in electric conduction and thermal conduction, Flip Chip Package is the common option and it occupies less package volume.
Referring to FIG. 1 and FIG. 2, cross-sectional views showing a chip-on-chip package using a conventional flip-chip technology, chips 110 and 220 are first bonded by bumps 130 and then it undergoes the process of filling underfill 140 into the gap between the chips 110 and 120, in which a less-viscous polymer fluid is first applied onto the chip 120 adjacent to the chip 110 and then this less-viscous polymer fluid inflows the gap between the chips 110 and 120 via capillary action.
However, using less viscous polymer fluid as the underfill 140 will cause the following drawbacks.
1. When the less viscous underfill 140 is filled into the gap between the chips 110 and 120, it further spreads outside the surrounding area of chip 110. Therefore, part of the underfill 140 after cured is left outside the surrounding area of chip 110. The underfill 140 flows even further onto another chip pad 122 for being subsequently wirebonded thereto due to the underfill 140 having less viscosity and higher fluidity, as shown in FIG. 1.
2. In order to prevent the underfill 140 from polluting the chip pad 122 adjacent to the chip 110, it is necessary to relocate chip pad 122 far away from the chip 110. This will introduce a great deal of limitation to the design for relocating the chip pad 122 of the chip 120.
3. It is very inefficient by this way to fill the underfill 140 into the gap between the chips 110 and 120 when multiple of the chips 110 need to be bonded with multiple of the chips 120 on a wafer. Because it takes many steps to fill the underfill 140 into the gaps between each of the chips 110 and each of the chips 120 on a wafer. As a result, low productivity can be expected.